First description of the sexual stage ofVenturia effusa, causal agent of pecan scab

Pecan scab, caused byVenturia effusa, is the most prevalent disease of pecan in the southeastern United States. Recent characterization of the mating type (MAT) distribution ofV. effusarevealed that theMATidiomorphs are in equilibrium at various spatial scales, indicative of regular sexual recombination. However, the occurrence of the sexual stage ofV. effusahas never been observed, and the pathogen was previously considered to rely entirely on asexual reproduction. We were able to generate the sexual stage by pairing isolates of opposite mating types on oatmeal culture media. Cultures were incubated at 24 C for 2 mo to allow hyphae from isolates of each mating type to interact. Culture plates were then incubated at 4 C for 4 mo, after which immature pseudothecia were observed. Following exposure to a 12-h photoperiod for 2 wk at 24 C, asci and ascospores readily developed. Pseudothecium and ascospore production was optimal when incubated for 4 mo at 4 C. We utilized progeny from a cross of an albino isolate and wild-type (melanized) isolates to determine that recombination had occurred. Multilocus genotyping using 32 microsatellite markers confirmed that progeny were the result of recombination, which was further supported by segregation of mating types and culture pigmentation. Albino progeny were all confirmed to contain the same mutation in the polyketide synthase (PKS1) melanin biosynthesis gene as the albino parent. The results of this study demonstrate the heterothallic nature ofV. effusa. The impact of determining the source of the overwintering ascostroma will aid in management decisions to reduce the primary inoculum in the disease cycle.